Centrifugal sifter apparatus

ABSTRACT

A centrifugal sifter comprises a rotor mounted for rotation within a housing and having a central material inlet zone in communication with outwardly extending distributing passages leading to a sifting zone at which coarse material is discharged. Exhaust passages in the rotor communicate at one end with the sifting zone and extend radially inwardly. Discharge passages in the rotor establish communication between the exhaust passages and fines discharge openings located adjacent the periphery of the rotor.

United States Patent 1191 Wessel June 24, 1975 [54] CENTRIFUGAL SIFTER APPARATUS 3,491,879 1 1970 Lapple 209 144 3,708, 67 1 I973 J O9 [76] Inventor: Josef Wessel, Am Sonnenhof I54, 1720313 35|973 6 7: Auflflrchm Germany 3,73l,800 5/1973 Timson 209/144 x 1 Filed: 1974 FOREIGN PATENTS OR APPLICATIONS [21] Appl. No.: 512,744 1,267,522 5/1968 Germany 209/144 RltedU.S.A l' t D ta pp ma a Primary ExaminerFrank W. Lutter [63] Contmuanon of Ser. No, 256,415, May 24, 1972,

abandoned Assistant Examiner-Ralph J. Hlil Attorney, Agent, or FirmLearman & McCulloch [30] Foreign Application Priority Data Feb. 3, 1971 Germany 2104967 ABSTRACT I A centrifugal sifter comprises a rotor mounted for ro- [52] US. Cl. 209/144 tation i i a housing and having a central material [51] Int. Cl B07b 7/83 inlet Zone in communication with outwardly extending [58] Field of Search t. 209/ 144, I45 distributing passages w i to a ifti zone at which coarse material is discharged. Exhaust passages in the References Clled rotor communicate at one end with the sifting zone UNITED STATES PATENTS and extend radially inwardly. Discharge passages in 2,270,143 1/1942 Schaich 209/144 x the rotor establish Communication between the 2,276,76l 3/1942 Carey 209/144 hauSt passages and fines discharge openings located 2338,77) l/l944 Mutch 209/144 adjacent the periphery of the rotor. 2,796,]73 6/1957 Payne et al. 209/]44 3.37|,782 3/1968 Meyer et al 209 144 21 Claims, 7 Drawing Figures \1 'I/f [Illa 'I I 4 s [If/,4 0

SHEET PATENTEnJunu m5 PATENTEDJUN 24 I975 SHEET PATENTED Jun 24 ms SHEET 1 C ENTRIF UGAL SIFTER APPARATUS This is a continuation of application Ser. No. 256,4l5, filed in the U.S. Patent Office on May 24, 1972, now abandoned.

The invention relates to a centrifugal sifter comprising a rotor which rotates within a housing and is charged centrally with material to be sifted, the rotor having material distributing passages which lead the material outwardly to sifting zones from which the fine material, which is deflected inwardly again, passes to discharge openings of the rotor.

In a known centrifugal sifter of the general class to which the invention relates (see German specification 1,267,522) the fines discharge openings of the rotor are disposed in the vicinity of the axis. The main disadvantage of such an arrangement is that for a given rotor diameter the total cross-section of the exhaust openings and thus the throughput capacity of the sifter (of air and material) is limited, i.e. is relatively small.

A centrifugal sifter according to the invention is constructed in such manner that for a given rotor diameter a substantial increase in the throughput capacity is obtained.

According to the invention, this objective is obtained by arranging fines discharge openings in the vicinity of the rotor periphery.

For a given rotor diameter this makes it possible to increase the cross-section and/or number of fines discharge openings and thus increase the throughput capacity of the sifter. Furthermore, by increasing the rotor diameter and the number of sifting zones while retaining the geometry of said zones a further increase in the throughput capacity can be obtained without having to accept any substantial increase in the coarseness of the separation limit.

According to a further development of the invention substantially U-shaped exhaust and discharge passages are provided betweer the sifting zones and the associated suction openings of the rotor. The U-shaped deflection decreases the influence of the exhausting taking place in the axial direction of the rotor. This makes the flow profile in the sifting zones more uniform, increasing the separation sharpness or permitting a further increase of the air and material throughput capacity by widening the exhaust passages in the axial direction of the rotorv According to a further feature of the invention the flow profile is made even more uniform over the width of the passages (i.e. over the dimension extending in the axial direction of the rotor) by providing at least one baffle plate. If several baffle plates are provided in the individual sifting zones they are conveniently arranged in such a manner that the outer edge ofa baffle plate is offset outwardly with respect to the outer edge of the preceding or leading baffle plate in the direction of rotation. This results in a particularly sharp deflection of the fine material in the sifting zones. This prevents individual coarse material particles from being discharged with the fine material flow; on the other hand, the repeated sifting operation at the staggered baffle plates provides thorough cleaning of the coarse material from fine material adhering thereto.

These and further features of the invention will be apparent from the following description of illustrative embodiments of the invention illustrated in the drawings, wherein:

FIG. 1 shows a vertical section through a centrifugal sifter according to the invention with vertical rotor axis;

FIG. 2 shows a partial section through the rotor along the line II-II of FIG. 1;

FIG. 3 shows a vertical section through a centrifugal sifter according to the invention with horizontal rotor axis;

FIG. 4 is a plan view of the sifter according to FIG.

FIGS. 5, 6 and 7 show details of three further em bodiments.

The centrifugal sifter illustrated in FIGS. 1 and 2 comprises a housing 1 within which is a rotor 2 rotatable by a motor 3 about a vertical axis 4.

The rotor 2 consists of two circular discs 5 and 6 with shaped passage-forming members 7 disposed therebetween which may, for example, be lengths of extruded profile sections. The discs 5, 6 and the shaped members 7 are held together by screws 8.

The upper disc 6 of the rotor 2 is provided with a central inlet opening 9 forming an inlet zone which is adjoined at the top by a collar 10 into which projects a feed pipe 11 for the material to be sifted.

Disposed stationary in the housing 1 beneath the rotor 2 is a collection chamber I3 supported by struts 12 in the housing I, to which chamber is connected a pipe 14 which serves to carry off the sifting air and the fine material and which leads to a fine material separator (not illustrated), for example a cyclon, and a following fan (also not illustrated).

Between adjacent shaped members 7 are open ended distributing passages 15 for the material to be sifted which lead the material from the inlet zone outwardly to the sifting zones 16. The members 7 have inwardly and outwardly extending, U-shaped exhaust and discharge passages 17 leading from the sifting zones I6 to discharge openings 18 which are provided in the lower disc 5 of the rotor 2. As is apparent in particular from FIG. 2, these discharge openings 18 are disposed in the vicinity of the rotor periphery. They are in open communication with the collecting chamber 13 disposed therebelow. Disposed between the material inlet zone and the distributing passages 15 are rod-like members 19 which serve to break up agglomerates of material.

The axes 20 of the distributing passages 15 form tangents to an imaginary circle 21 around the rotor axis, the axes 20 of said passages 15 having an inclination trailing the direction of rotation (arrow 22).

The discs 5, 6 of the rotor 2 project somewhat beyond the periphery defined by the shaped member 7. This provides improved flow of the sifting air into the sifting zones.

The mode of operation of the example of embodiment illustrated in FIGS. 1 and 2 is as follows:

The sifting air (arrow 23) enters through the coarse material hopper la of the housing 1, passes through the sifting zone 16 from the outside, passes through the exhaust and discharge passages 17 and the discharge openings 18 into the collecting chamber 13 and is sucked off via the pipe 14 and the dust separator (not illustrated) by the fan (also not illustrated).

The sifting material (arrow 24) is introduced into the rotor 2 centrally and thrown outwardly in the distributing passages 15 under the action of the centrifugal force and the Coriolis force. In the region of the sifting zone 16 the fine material is sharply deflected by the sifting air flowing substantially radially inwardly and carried off with the air through the exhaust and discharge passages 17, the discharge openings 18, the collecting chamber 13 and the pipe 14 (arrow 24a). The coarse material (arrow 24b) on the other hand is car.- ried outwardly out of the sifting zones 16 and led off through the coarse material hopper la of the housing. A large part of the coarse material is centrifuged in the sifting zone against the wall thereof following in the direction of rotation so that any agglomerates still present are broken up and fine particles are sifted out. On leaving the housing the coarse material is subjected to another sifting by the counterflowing air.

FIGS. 3 and 4 show an example of embodiment of a centrifugal sifter according to the invention having a horizontal rotor axis 4'. The housing I is of substantially spiral form and is provided at its periphery with two substantially tangential openings 25 for the inlet of the sifting air and an opening 26 for the inlet of sifting air and discharge of coarse material. The collecting chamber 13' for discharging the air and the fine material adjoins the disc 5 of the rotor 2 provided with the discharge openings 18, said rotor otherwise being constructed as in the previously described embodiment. The material to be sifted is supplied via a pipe 11' through a central opening 9 in the disc 6 of the overhung-mounted rotor 2.

In the operation of this embodiment, the sifting air (arrow 23) enters the housing 1' through the openings 25, 26, then passes in the manner explained with reference to FIGS. 1 and 2 through the rotor 2 and is then led through the chamber 13' and discharged through the following pipe 14 with the fine material. The material to be sifted (arrow 24) passes through the inlet pipe 11 into the rotor 2 and is sifted in the sifting zones in the manner already described. The fine material (arrow 24a) is led off with the air through the collecting chamber 13' and the pipe 14' and the coarse material (arrow 24b) leaves the housing 1' through the opening 26.

In the modification illustrated in FIG. 5 there is disposed in each of the individual sifting zones 16' a baffle plate 27 which is adjustable about an axis 28 extending parallel to the axis of rotation of the rotor. Such a baffle plate enables a uniform flow profile to be obtained over the axial widths of the sifting zone. In the embodiment of FIG. 6 a plurality (for example 2) of baffle plates 29, 30 are disposed in the individual sifting zones 16'', the outer edge of the trailing baffle plate 30 being outwardly offset with respect to the leading baffle plate 29, considered in the direction of rotation (arrow 22). This gives a staggered deflection of the fine material which provides a particularly high separation sharpness.

FIG. 7 shows an embodiment in which the discharge openings 18' are disposed between hairpin-shaped ribs 31 and the combined exhaust and discharge passages between the sifting zones 16" and the discharge openings 18 are kept quite short. In this embodiment as well the fine particles of the material fed through the distributing passages are sharply deflected in the region of the individual sifting zones 16", being supplied with the sifting air (arrow 23) flowing from the outside to the opening 18', the coarse material being carried outwardly.

In this embodiment the ribs 31 following each other in the peripheral direction are of different lengths so that the outer portion of the longer ribs acts firstly as a baffle plate and secondly renders uniform the flow conditions in the sifting zones 16". Embodiments having ribs of equal length are of course also possible within the scope of the invention.

In the embodiment of FIG. 7 the rotor is preferably made with a large diameter and small axial dimensions.

Wear-resistant lining is preferably provided on the rotor at the areas subjected to the friction and/or impact of the material to be sifted in all embodiments.

Within the scope of the invention embodiments are possible in which at least two systems of distributing passages, sifting zones and exhaust openings are arranged in series in the axial direction in mirror-image relationship, each system being provided with an associated collecting chamber for fine material and sifting air, charging means common to all systems advantageously being provided on one side and the overhung mounting of the rotor on the other.

Within the scope of the invention it is possible for the distributing passages to extend to the rotor periphery so that the sifting zones lie outside said periphery.

I claim:

1. Centrifugal sifter apparatus comprising a housing having an air inlet for sifting air and outlets for coarse and fine materials, respectively; a rotor mounted within said housing for rotation about an axis; means for introducing material to be sifted to said rotor at an inlet zone in the vicinity of said axis; and means establishing a plurality of circumferentially spaced material distributing passages in said rotor and extending outwardly from said inlet zone to a sifting zone and a plurality of circumferentially spaced fine material discharge passages alternating with said distributing passages and extending inwardly from said sifting zone toward but terminating short of said inlet zone, each of said distributing passages having a fine material discharge opening therein extending axially of said rotor, each of said discharge openings occupying a position closer to the rotors periphery than to its axis of rotation.

2. Apparatus according to claim 1 wherein each of said discharge passages is substantially U-shaped.

3. Apparatus according to claim 1 including baffle means in said sifting zone.

4. Apparatus according to claim 3 wherein said baffle means comprises a single plate.

5. Apparatus according to claim 4 wherein said plate is adjustable about an axis parallel to the axis of rotation of said rotor.

6. Apparatus according to claim 3 wherein said baffle means comprises a plurality of plates.

7. Apparatus according to claim 6 wherein the radially outer edges of the trailing plates with reference to the direction of rotation of said rotor are radially outwardly offset with respect to the outer edges of the leading plates with reference to said direction of rotation of said rotor.

8. Apparatus according to claim 1 wherein said rotor comprises a pair of discs spaced from one another by the passage-forming means.

9. Apparatus according to claim 8 wherein said discs project beyond the passage-forming means.

10. Apparatus according to claim I wherein the surfaces of said rotor and the passage-forming means engageable by material to be sifted are provided with wear-resistant lining material.

11. Apparatus according to claim 1 wherein said rotor is rotatable about a vertical axis.

12. Apparatus according to claim 1 wherein said rotor is rotatable about a horizontal axis.

13. Apparatus according to claim 1 wherein said housing is of substantially spiral form and wherein said air inlet opening is substantially tangential to the periphery of said housing.

14. Apparatus according to claim 1 wherein said air inlet also constitutes a discharge opening for coarse material.

15. Apparatus according to claim 1 wherein the axis of each of said distributing passages is tangent to an imaginary circle around the axis of said rotor and is inclined in a direction trailing the direction of rotation of said rotor.

16. Apparatus according to claim 1 including means carried by said rotor between said material introducing means and said distributing passage for breaking up agglomerated material.

17. Apparatus according to claim 1 wherein the means forming each of said discharge passages comprises a hairpin-shaped rib.

18. Apparatus according to claim 17 wherein successive limbs of said rib peripherally of said rotor have different lengths.

l9. Apparatus according to claim 1 wherein said distributing passage is open at its radially outer end and wherein said sifting zone lies outwardly of said rotor.

20. A centrifugal sifter apparatus comprising a housing provided with an inlet for sifting air, an outlet for coarse material, and an outlet for fine material; a rotor mounted within said housing for rotation about an axis, said rotor comprising a pair of discs spaced from one another; means for introducing material to be sifted into said rotor at a central inlet zone in the vicinity of said axis; and shaped members interposed between said discs and forming therebetween a plurality of material distributing passages extending outwardly from said central inlet zone to peripheral sifting zones, one of said discs having therein a plurality of axial discharge openings adjacent the periphery of said rotor and located closer to the periphery of said rotor than to its axis of rotation, said shaped members also forming a plurality of U-shaped fine material discharge passages between said discs and extending from said sifting zones to said discharge openings, said distributing passages being peripherally spaced from said discharge passages.

21. Apparatus according to claim 20 wherein said distributing passages and said discharge passages are co-planar. 

1. Centrifugal sifter apparatus comprising a housing having an air inlet for sifting air and outlets for coarse and fine materials, respectively; a rotor mounted within said housing for rotation about an axis; means for introducing material to be sifted to said rotor at an inlet zone in the vicinity of said axis; and means establishing a plurality of circumferentially spaced material distributing passages in said rotor and extending outwardly from said inlet zone to a sifting zone and a plurality of circumferentially spaced fine material discharge passages alternating with said distributing passages and extending inwardly from said sifting zone toward but terminating short of said inlet zone, each of said distributing passages having a fine material discharge opening therein extending axially of said rotor, each of said discharge openings occupying a position closer to the rotor''s periphery than to its axis of rotation.
 2. Apparatus according to claim 1 wherein each of said discharge passages is substantially U-shaped.
 3. Apparatus according to claim 1 including baffle means in said sifting zone.
 4. Apparatus according to claim 3 wherein said baffle means comprises a single plate.
 5. Apparatus according to claim 4 wherein said plate is adjustable about an axis parallel to the axis of rotation of said rotor.
 6. Apparatus according to claim 3 wherein said baffle means comprises a plurality of plates.
 7. Apparatus according to claim 6 wherein the radially outer edges of the trailing plates with reference to the direction of rotation of said rotor are radially outwardly offset with respect to the outer edges of the leading plates with reference to said direction of rotation of said rotor.
 8. Apparatus according to claim 1 wherein said rotor comprises a pair of discs spaced from one another by the passage-forming means.
 9. Apparatus according to claim 8 wherein said discs project beyond the passage-forming means.
 10. Apparatus according to claim 1 wherein the surfaces of said rotor and the passage-forming means engageable by material to be sifted are provided with wear-resistant lining material.
 11. Apparatus according to claim 1 wherein said rotor is rotatable about a vertical axis.
 12. Apparatus according to claim 1 wherein said rotor is rotatable about a horizontal axis.
 13. Apparatus according to claim 1 wherein said housing is of substantially spiral form and wherein said air inlet opening is substantially tangential to the periphery of said housing.
 14. Apparatus according to claim 1 wherein said air inlet also constitutes a discharge opening for coarse material.
 15. Apparatus according to claim 1 wherein the axis of each of said distributing passages is tangent to an imaginary circle around the axis of said rotor and is inclined in a direction trailing the direction of rotation of said rotor.
 16. Apparatus according to claim 1 including means carried by said rotor between said material introducing means and said distributing passage for breaking up agglomerated material.
 17. Apparatus according to claim 1 wherein the means forming each of said discharge passages comprises a hairpin-shaped rib.
 18. Apparatus according to claim 17 wherein successive limbs of said rib peripherally of said rotor have different lengths.
 19. Apparatus according to claim 1 wherein said distributing passage is open at its radially outer end and wherein said sifting zone lies outwardly of said rotor.
 20. A centrifugal sifter apparatus comprising a housing provided with an inlet for sifting air, an outlet for coarse material, and an outlet for fine material; a rotor mounted within said housing for rotation about an axis, said rotor comprising a pair of discs spaced from one another; means for introducing material to be sifted into said rotor at a central inlet zone in the vicinity of said axis; and shaped members interposed between said discs and forming therebetween a plurality of material distributing passages extending outwardly from said central inlet zone to peripheral sifting zones, one of said discs having therein a plurality of axial discharge openings adjacent the periphery of said rotor and located closer to the periphery of said rotor than to its axis of rotation, said shaped members also forming a plurality of U-shaped fine material discharge passages between said discs and extending from said sifting zones to said discharge openings, said distributing passages being peripherally spaced from said discharge passages.
 21. Apparatus according to claim 20 wherein said distributing passages and said discharge passages are co-planar. 